1. Field of the Invention
The present invention finds principal application within the field of passive solar energy systems. More particularly, the invention relates to a thermosiphon solar energy system which is suitable for preheating water.
2. Prior Art
With the dwindling supplies of fossil fuel and the accompanying increasing energy cost, extensive research efforts are being focused to harness solar radiation on a practical and economical scale. One type of device which shows promise in the field is the thermosiphon system, described in U.S. Pat. Nos. 4,137,964 and 4,050,508, issued to Bruce Shawn Buckley. As disclosed in the above references, a "thermic diode" panel is used to collect and store the sun's radiant energy. The panel typically comprises a shallow, rectangular box that is effectively divided into two chambers by a slab of insulation. The chambers are filled with a liquid, such as water, and are in open communication with each other at the bottom of the panel via a passage through the insulation, and in open communication at the top through an "oil valve" control box, normally located outside the panel proper.
Solar radiation, incident on the outer panel face, will heat the water in the collector chamber. As the water is heated, it expands and passes upwardly through the oil valve and into the cooler storage chamber, setting up a thermosiphon loop. Cooler water from the storage chamber, in turn, passes through the insulation passage at the bottom of the panel to the warmer collector chamber.
If such a panel is used during the day to collect solar energy and store the heat for nighttime use, reverse thermosiphoning must be avoided to prevent energy loss. The oil valve achieves this objective and, in addition, increases the sensitivity of the thermosiphoning process to small temperature differences between the chambers. However, loss of the oil to solution presents certain problems, and the use of a demand water exchanger, as shown in U.S. Pat. No. 4,050,508, requires a rather large heat exchange surface area to be effective, which in turn increases the overall unit cost.
It is, therefore, an objective of the present invention to provide an inexpensive but reliable alternative to the oil valve and to provide a hot water preheater system incorporating the alternative valve without the use of a large heat exchange surface area.